Subtropical Eastern North Pacific SST Bias in Earth System Models. Issue 8 (28th July 2021)

• Record Type: Journal Article
• Authors: Balaguru, Karthik; Van Roekel, Luke P.; Leung, L. Ruby; Veneziani, Milena
• Is Part Of: Journal of geophysical research. Volume 126:Issue 8(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-07-28
• Subjects: CMIP6 -- coupled climate models -- Eastern Pacific -- large‐scale circulation -- mixed‐layer heat budget -- SST biases; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2021JC017359
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: This study systematically evaluates the warm sea surface temperature (SST) bias in the Subtropical Eastern North Pacific, a problem plaguing most Coupled Model Intercomparison Project Phase 6 models, using the Energy Exascale Earth System Model version 1 (E3SM). In the model at its standard resolution (1° atmosphere, 30–60 km ocean), the SST bias, exceeding several degrees, is mainly concentrated along the coast between 25°N and 40°N. In the high‐resolution (0.25° atmosphere, 18–6 km ocean) version of the model, the nearshore SST bias improves considerably with a better representation of coastal upwelling. However, the offshore SST bias, approximately centered at 125°W and 25°N, is relatively stronger in the high‐resolution version. To better understand the offshore warm bias in the model, a mixed‐layer heat budget analysis is performed. While errors in surface radiative fluxes occur at both resolutions, positive biases in horizontal heat advection also play a role in the SST bias at high‐resolution. Analysis of HighResMIP models indicates that the shift in the location of the prominent SST bias from nearshore to offshore with an increase in model spatial resolution, is not native to E3SM alone. Plain Language Summary: Most coupled climate models suffer from warm sea surface temperature (SST) biases near subtropical eastern boundary regions in the global oceans. Despite numerous improvements in models over time, these problems have persisted. While previous studies focused on understanding the bias in the Southeast Atlantic and Southeast Pacific, a thorough evaluation of the bias for the Subtropical Eastern North Pacific (SENP) has not been performed. In this study, we address this issue using fully coupled and forced simulations, at different resolutions, using the Energy Exascale Earth System Model version 1 (E3SM). At standard resolution (∼1° atmosphere, ∼0.4° ocean), a warm SST bias exceeding several degrees occurs predominantly along the coast. At high resolution (∼0.25° atmosphere, ∼0.1° ocean), the nearshore bias improves considerably due to a better representation of coastal processes but the offshore bias degrades further. While errors in surface radiative fluxes due to misrepresentation of stratus clouds affect the offshore bias at both resolutions, errors in upper‐ocean heat transport associated with surface wind biases also plays a role at high resolution. Finally, the mechanisms causing the SENP SST bias in E3SM may also operate in other climate models. Key Points: The nearshore warm sea surface temperature (SST) bias in the Subtropical Eastern North Pacific (SENP) improves with resolution in Energy Exascale Earth System Model (E3SM) due to a better simulation of coastal upwelling The offshore SENP SST bias becomes worse with an increase in resolution in E3SM due to errors in horizontal advection Results based on E3SM are consistent with those from Coupled Model Intercomparison Project Phase 6 and HighResMIP, highlighting their broad nature